The process commonly practiced for the production of phenol involves the oxidation of cumene to cumene hydroperoxide, followed by its acid catalyzed decomposition to phenol and acetone. Isolation of phenol from the reaction product involves the neutralization of the acid catalyst, followed by a series of distillation and separation steps. The lower boiling components such as acetone, unreacted cumene as well as α-methylstyrene (AMS) are first recovered from the crude product by distillation. The remaining material is introduced into a phenol recovery column in which phenol is distilled away from the higher boiling impurities. Depending on the distillation procedures used to recover acetone, cumene and AMS, the distilled phenol may contain minor quantities of impurities such as mesityl oxide (MO), acetol (hydroxyacetone) and other aliphatic carbonyl compounds, olefinic compounds, acetophenone, cumylphenols and 2- and 3-methylbenzofuran (MBF) in addition to residual amounts of acetone, cumene and AMS. Such impurities are undesirable in phenol used in certain applications such as in the manufacture of bisphenol-A.
MBF is a particularly undesirable contaminant of phenol that is used for certain applications such as in the production of bisphenol-A, a precursor to polycarbonate resins. Due to similar volatility, MBF cannot be separated from phenol by fractional distillation. U.S. Pat. Nos. 5,064,507 and 4,857,151 describe a process of distillation in the presence of water (also called steam stripping) to reduce MBF in phenol. However, due to the high energy costs and the necessity to use large distillation columns, this process is expensive in terms of capital investment and operating costs. U.S. Pat. No. 5,414,154 describes the use of a strong acid ion exchange resin to reduce the level of MBF by converting it to higher boiling compounds. U.S. Pat. No. 5,414,154 also showed that the effectiveness of MBF removal by resin treatment increases with an increase in temperature.
Although strong acid ion exchange resins also remove carbonyl compounds from phenol on contact, acetol reacts with phenol to produce more MBF. U.S. Pat. No. 5,414,154 teaches the necessity to remove acetol from phenol (e.g. by treatment with an amine) prior to contact with the resin to remove MBF.
Although effective, amine treatment involves the use of an expensive reagent, which must subsequently be purged from the phenol stream.
Both U.S. Pat. Nos. 3,810,946 and 6,489,519 disclose treatment of a phenol stream containing acetol with an acid or acid resin to remove acetol. British Patent 0 865 677 discloses a process for removing acetol from a phenol stream wherein the phenol stream is heated in the presence or absence of a catalyst. However, in all of these patents, acetol is removed by reacting it with phenol to form MBF, which is subsequently purged from the phenol stream.
European Patent 0 004 168 and U.S. Pat. No. 4,857,151 disclose distillation processes to remove acetol from phenol streams. However, these methods involve the use of capital intensive distillation apparatus.
There remains a need for an efficient, low cost method for the removal of acetol from a phenol stream that does not adversely affect phenol yields by formation of significant amount of additional MBF.